Doppler Effect on Location-Based Tracking in Mobile Sensor Networks Mohamed Hamdi, Ramzi Bellazreg, Noureddine Boudriga Communication Networks and Security Research Lab. University of 7 th of November at Carthage, Tunisia {mmh,nab}@supcom.rnu.tn Abstract Mobile Sensor Networks (MSNs) consist of large number of small and computationally impoverished devices deployed over an area to track mobile objects. Mobility is becoming an important feature of MSNs. Recently, sensors have began to be deployed on mobile platforms such as robots. In this paper, we propose an evaluation of the mobility impact on MSN tracking efficiency. More precisely, we consider the Doppler effect on the results of several target location approaches. Two radar-based angle estimation techniques have been considered: Frequency-Modulated Continuous Wave (FMCW) Radar, and monopulse angle estimation. We also analyze the control of the uncertainty due to Doppler shift through a manipulation of the area coverage (i.e., number of sensors per area coverage). 1. Introduction Mobile Sensor Networks (MSNs) consist of large number of small and computationally impoverished devices deployed over an area to track mobile objects. Depending on the nature of the target, different sensing techniques may be used such as those based on temperature, light, sound or ultra-sound waves. Particularly, when the object of interest is a vehicle, radar (Radio Detection and Ranging) systems show an important efficiency. Moreover, the event that characterizes a detected object may vary according to the sensing approach. For instance, the sensor may generate only one bit of information to indicate whether the target is within its range or not. Angular techniques can also be used to track the angular location of a mobile object. Finally, more precise sensing techniques allow estimating the exact location of the target. Mobility is becoming an important feature of MSNs. Recently, sensors have began to be deployed on mobile platforms such as robots. This turns out to be useful in situations where the sensors operate in a hostile environment. In addition, researches have demonstrated that sensor motion may enhance the network coverage. Nevertheless, when both sensors and targets are mobile, the frequency and the power of the reflected signals might be affected by the relative velocity. In this paper, we propose an evaluation of the mobility impact on MSN tracking efficiency. More precisely, we consider the Doppler effect on the results of several target location approaches. Two radar-based angle estimation techniques have been considered: Frequency-Modulated Continuous Wave (FMCW) Radar [1], and monopulse angle estimation [2, 3]. We perform a statistical analysis of the relation between the target-location uncertainty and the relative speed of the target with respect to the sensor. To the best of our knowledge, the evaluation of the Doppler frequency shift on the accuracy of the events generated by a MSN has not been previously addressed by researchers. In fact, an important fact that should be necessarily taken into consideration is that, even though the mobility of the sensor nodes can be monitored by some central nodes of the MSN, there is no possible control on the target motion. In the following, we show that the quality of the information about on the correctness of the estimated angle depends on the available knowledge about the target mobility model. We also analyze the control of the uncertainty due to Doppler shift through a manipulation of the area coverage (i.e., number of sensors per area coverage). The rest of the paper is organized as follows. Section 2 reviews the two aforementioned angle estimation techniques. Section 3 describes the mobility impact on MSN efficiency. Particularly, the frequency shift due to the relative mobility of target with respect to the antenna elements (i.e., sensor node) will be addressed. The importance of coverage aspects is highlighted in Section 4. Finally, Section 5 concludes the paper. 2. Angle-based location estimation techniques This section describes two approaches that have been proposed in the literature to determine the angular location of a target. The first is based on analyzing the 252 1-4244-1031-2/07/$25.00©2007 IEEE